Table 1.

Change in SR Ca²⁺ content in skinned fibres equilibrated in pCa 7.3 solution

	Initial Ca2+ content		Ca2+ content after equilibration
	(% of maximal)	(% of endogenous)	(% of endogenous)	(% of Initial)	CSQ1 (% av EDL)	CSQ2 (% av SOL)	SERCA1 (% av EDL)
EDL fibres (n= 5)	18 ± 4	124 ± 11	110 ± 18	88 ± 15	75–102	0	80–140
SOL (I) fibres (n= 6)	60 ± 2†	99 ± 7	121 ± 8	123 ± 3*	16–43	70–130	0–1

As in Fig. 6, each EDL or SOL (I) fibre was loaded to a set level (initial Ca²⁺ content), similar to that present endogenously, and the change in SR Ca²⁺ content after a 2 min equilibration period at pCa 7.3 was assessed from the area of the force response upon emptying the SR (relative to bracketing control measurements). † Maximal content was not measured in 2 SOL fibres, and indicated mean value is for 4 fibres only. Ranges of CSQ1, CSQ2 and SERCA1 amounts found in each segment are shown relative to average level in EDL or SOL (I) fibres. Calsequestrin and SERCA1 densities were not measured in 1 EDL fibre. Soleus type I fibres significantly increased SR Ca²⁺ content in the pCa 7.3 solution (*P < 0.05, Student's paired t test), whereas EDL fibres showed no significant change. Note that ‘% av’ is the percentage of the average value found across all the EDL or SOL fibres on the same gel.